DE69811420T2 - Grinding machine and process - Google Patents

Description

BACKGROUND OF THE INVENTION

The present invention relates to a grinding machine and a grinding method for highly accurately grinding at least one side of a hard and thin workpiece, for example a wafer used for a semiconductor device.

Generally, a conventional grinding machine has spindles that are rotatably supported by spindle heads thereof such that a grinding wheel is fixed to a front end of each spindle. Further, a feed unit comprising a motor and a ball screw is connected to the spindle head. When the spindle heads are fed by the feed units and moved in the axial direction while the grinding wheels are rotated by the rotating motors, the outer surfaces of the workpiece are ground.

The conventional grinding machine is constructed such that each grinding wheel feeding unit includes the motor and the ball screw. When the ball screw is rotated by the motor, the spindle head feeding operation is performed. However, the grinding wheels cannot be fed accurately due to insufficient rigidity of the machine and frictional resistance of sliding portions when the feeding operation must be performed precisely in the micrometer or submicron order. Therefore, a problem arises that precision grinding operation cannot be performed.

For example, as a grinding machine capable of grinding both side surfaces of the workpiece, Japanese Utility Model Examined Publication No. Hei. 1-8282 teaches a conventional double-head grinding machine. The grinding machine disclosed therein has a structure in which a C-shaped column frame, which can project from the frame of the grinding machine in a cantilever manner, forms a grinding head that supports the upper grinding wheel. A bending moment acts due to a reaction force during grinding, which is due to a grinding resistance that occurs at the machining operation, acts on the grinding wheel, on the column. Furthermore, heat deformation occurs so that accurate grinding is prevented. Therefore, a frame having an upper bed arranged above a lower bed has been disclosed. Further, the upper and lower grinding wheels provided on the mentioned frame are attached to upper and lower spindles. The spindles are rotated by motors and rings arranged on the sides of the spindles. The upper spindle is moved vertically by a feed device comprising a rack operated by hydraulic pressure or air pressure.

As a means for vertically moving the upper grinding wheel, a structure has been disclosed in, for example, Japanese Unexamined Patent Publication No. Sho. 61-270043. The means includes a feed device that vertically moves spindle heads with motors, ball screws and nuts provided for the spindle heads. The main spindle is supported in the spindle head by a hydrostatic bearing. Further, each grinding wheel is rotated by a built-in motor.

The conventional grinding machine as disclosed in the above-mentioned Japanese Unexamined Patent Publication No. Sho. 61-270043 has a frame which is free from thermal deformation and a rotating support by which the main spindles do not undergo thermal expansion. Furthermore, this conventional grinding machine has the feed mechanism which includes the rack or the ball screw which is operated by the motor serving as the drive source and which is constructed so that the grinding heads are guided vertically along the sliding surfaces, so that there is a problem that the conventional grinding machine cannot substantially perform accurate feed due to sliding resistance and the like.

Furthermore, in the conventional grinding machine, the motors, which are driving sources for vertically moving the grinding heads, and the ball screws are arranged on the sides of the spindles for rotating the grinding wheels, so that a transverse force acts on the spindle. Accordingly, it is very likely that that smooth and precise feed cannot be carried out and interrupted.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the problems encountered in the conventional methods.

An object of the present invention is to provide a grinding machine and a grinding method with which grinding wheels can be accurately fed and moved to predetermined grinding positions for grinding a hard material such as a semiconductor wafer.

Furthermore, it is an object of the present invention to provide a grinding machine and a grinding method that ensure sufficient rigidity and enable a precise grinding process to be carried out.

Furthermore, it is an object of the present invention to provide a dual-head type grinding machine with which the levelness (horizontal inclination) of the grinding wheel can be adjusted so that the two side surfaces of a workpiece are accurately ground and become parallel.

The object of the present invention can be achieved with a grinding machine, which comprises:

a first grinding wheel drive unit standing upright in a vertical direction, the first grinding wheel drive unit including a first spindle that is rotatable, and a first housing that rotatably supports the first spindle;

a first grinding wheel held at one end of the first spindle;

a first feed device that moves the first housing in the vertical direction, the first feed device having a mechanism for converting rotational motion into linear motion; and

a first hydrostatic radial bearing movably supporting the first housing.

In the above construction of the grinding machine according to the present invention, the first feed means preferably includes a motor, a ball screw and a nut portion connected to each other, and the ball screw is arranged coaxially with the first housing.

In the above construction of the grinding machine according to the present invention, the first grinding wheel unit preferably comprises:

a second hydrostatic radial bearing provided in the first housing for directly and rotatably supporting the first spindle; and

a first hydrostatic thrust bearing rotatably supporting the first spindle.

The above-mentioned construction of the grinding machine according to the present invention more advantageously further comprises:

a first auxiliary feed device that moves the first spindle in a vertical direction, the first auxiliary feed device having a first pressure regulating mechanism that can regulate the pressure of a fluid in the first hydrostatic thrust bearing that rotatably supports the first spindle.

In the above construction of the grinding machine according to the present invention, the first hydrostatic radial bearing preferably comprises a plurality of hydrostatic radial bearing sections separated from each other in the vertical direction.

The above-mentioned construction of the grinding machine according to the present invention advantageously further comprises:

a second grinding wheel drive unit arranged opposite to the first grinding wheel drive unit and standing upright in a vertical direction, wherein the second grinding wheel drive unit includes a second rotatable spindle and a second housing rotatably supporting the second spindle;

a second grinding wheel held at one end of the second spindle in a state in which the second grinding wheel is held substantially parallel to and opposite to the first grinding wheel; and

a second feed device that moves the second housing in the vertical direction, the second feed device having a mechanism for converting rotational motion into linear motion; and

a third hydrostatic radial bearing which movably supports the second housing.

In the above construction of the grinding machine according to the present invention, the second feed device advantageously comprises a motor, a ball screw and a nut portion which are connected to each other, and the second housing is arranged coaxially with the ball screw.

In the above construction of the grinding machine according to the present invention, the second housing advantageously comprises:

a fourth hydrostatic radial bearing rotatably supporting the second spindle; and

a second hydrostatic axial bearing which rotatably supports the second spindle.

The above-mentioned construction of the grinding machine according to the present invention advantageously further comprises:

a second auxiliary feed device that moves the second spindle in a vertical direction, the second auxiliary feed device having a second pressure regulating mechanism that can regulate the pressure of a fluid in the second hydrostatic thrust bearing that rotatably supports the second spindle.

In the above construction of the grinding machine according to the present invention, the third hydrostatic radial bearing advantageously comprises a plurality of hydrostatic radial bearing sections separated from each other in the vertical direction.

It is further noted that the above object can be achieved by a grinding method comprising, according to the present invention, the following steps:

Feeding or feeding a housing which rotatably supports a spindle in a vertical direction, the housing being held by a hydrostatic radial bearing.

It is further noted that the above-mentioned object can be further achieved with a grinding machine which, according to the present invention, comprises:

an upper grinding wheel drive unit standing upright in the vertical direction;

an upper spindle rotatably disposed in the upper grinding wheel drive unit;

an upper motor that rotates the upper spindle;

an upper grinding wheel held at one end of the upper spindle;

an upper feed device having a mechanism for converting rotary motion into linear motion and moving the upper grinding wheel in the vertical direction, wherein:

the rotation axis of the upper motor, the rotation axis of the upper spindle, the rotation axis of the lower spindle and the axial line of the upper feed device are aligned with each other.

The above-mentioned structure of the grinding machine according to the present invention advantageously further comprises:

a precision feed device having a first pressure regulating mechanism capable of regulating the pressure of a fluid in a first hydrostatic thrust bearing that rotatably supports the first spindle and moves the first grinding wheel in the vertical direction, wherein

the axial line of the precision feed device is aligned with the axial line of the upper feed device.

It should further be noted that the above object can also be achieved with a dual-head grinding machine comprising according to the present invention:

an upper grinding wheel drive unit standing upright in the vertical direction;

an upper spindle rotatably disposed in the upper grinding wheel drive unit;

an upper motor that rotates the upper spindle;

an upper grinding wheel held at one end of the upper spindle;

an upper feed device having a mechanism for converting rotational motion into linear motion and moving the first grinding wheel in the vertical direction;

an upper precision feed device having an upper pressure regulating mechanism capable of regulating the pressure of a fluid in the upper hydrostatic thrust bearing that rotatably supports the upper spindle and moves the upper grinding wheel in the vertical direction;

a lower grinding wheel drive unit disposed opposite to the upper grinding wheel drive unit and standing upright in the vertical direction;

a lower spindle rotatably disposed in the lower grinding wheel drive unit;

a lower motor that rotates the lower spindle;

a lower grinding wheel supported at one end of the lower spindle such that the lower grinding wheel is maintained substantially parallel to and opposite the upper grinding wheel;

a lower feed device having a mechanism for converting rotary motion into linear motion and moving the lower grinding wheel in the vertical direction; and

a lower precision feed device having a lower pressure regulating mechanism capable of regulating the pressure of the fluid in the lower hydrostatic thrust bearing which rotatably supports the lower spindle and moves the lower grinding wheel in the vertical direction, wherein:

the rotation axis of the upper motor, the rotation axis of the lower motor, the rotation axis of the upper spindle, the rotation axis of the lower spindle, the axial line of the upper feed device, the axial line of the lower feed device, the axial line of the upper precision feed device and the axial line of the lower precision feed device are aligned with each other.

Furthermore, it should be noted that the above-mentioned object can also be achieved with a grinding machine comprising according to the present invention:

a grinding wheel drive unit standing upright in the vertical direction;

a spindle rotatably mounted in the grinding wheel drive unit;

a grinding wheel holder arranged at one end of the spindle; and

a horizontal inclination adjusting device that compensates the horizontal inclination of the grinding wheel holder by regulating the pressure of the fluid.

Furthermore, in order to achieve the object, according to an aspect of the present invention, there is provided a dual-head grinding machine having two grinding wheels that are moved in the axial direction, the two grinding wheels being rotated so as to grind a workpiece, the dual-head grinding machine comprising:

spindles for the grinding wheels arranged such that at least one of the spindles is rotatably supported by benches for the grinding wheels via a hydrostatic thrust bearing; and a pressure regulating device that regulates the pressure of a fluid supplied to at least one of supply ports formed in the hydrostatic thrust bearing and capable of communicating with each other in a direction of the axial line of the spindles in a direction opposite to each other.

When a workpiece is ground by the above-mentioned double-head grinding machine according to the present invention, the benches for the grinding wheels are rapidly fed to positions adjacent to the workpiece by the motors and the ball screws while the grinding wheels are rotated. Then, the feed mode is set to the feed for grinding so that the workpiece is ground to an extent close to a predetermined extent. Finally, the pressure regulating device regulates the pressure of the fluid supplied to at least one of the supply ports of the hydrostatic thrust bearing. Thereby, the bearing balance of the spindles in the axial direction established by the hydrostatic thrust bearing is changed so that the grinding wheels are precisely fed and moved to predetermined grinding positions.

In the above-mentioned double-head grinding machine according to the present invention, the pressure regulating device advantageously comprises a regulating device for changing the pressure by adjusting a throttling of the fluid.

Furthermore, the above-mentioned double-head grinding machine is advantageously constructed so that the pressure regulating means comprises a regulating means for setting a restriction of the pressure. When the pressure is changed by the regulating means, the pressure of the fluid supplied to the supply port of the hydrostatic thrust bearing can be easily regulated.

Furthermore, in order to achieve the above-mentioned objects, according to an aspect of the present invention, there is provided a dual-head grinding machine having grinding wheel drive units standing upright and including upper and lower spindles each rotatable by a motor and arranged so that upper and lower grinding wheels are held substantially parallel to and opposed to each other by the upper and lower spindles, and a workpiece is inserted into a space between the two grinding wheels so that the workpiece is rotated and ground, the dual-head grinding machine comprising: first feeding means provided for the upper and lower grinding wheel drive units and each having a mechanism for converting the rotary motion of the upper and lower grinding wheels into straight reciprocating motion so as to move the upper and lower grinding wheels vertically toward the workpiece; and a second feed device provided at least for the upper and lower grinding wheel drive units, the second feed device feeding the grinding wheel by fluid pressure over a short distance so as to carry out precise finishing of the workpiece.

The upper and lower grinding wheel drive units have the housing in the guide which stands upright. Furthermore, the spindle is rotatably arranged in the housing. In order to move the grinding wheel vertically with the first feed device, the housing is directly moved vertically by the first feed device. Since the mechanism for converting the rotary motion into the linear reciprocating motion is employed, the housing can be quickly fed so that it can approach the grinding wheel. Furthermore, the grinding wheel can be fed in an unchanged state so that the workpiece is ground.

The second feed device moves the spindle directly in the vertical direction. The second feed device is available for the upper and lower grinding wheel drive units, only the upper grinding wheel drive unit, or only the lower grinding wheel drive unit. Furthermore, a function is provided to perform feed in submicron units, which cannot be easily performed with the first feed device.

In the above-mentioned double-head grinding machine according to the present invention, the first feed means advantageously includes a motor, a ball screw and a nut portion, and the axial line of the ball screw is aligned with the axial lines of the upper and lower spindles.

In the above-mentioned double-head grinding machine according to the present invention, the second feed device advantageously supports the spindle with a hydrostatic thrust bearing and a hydrostatic radial bearing and changes the back pressure of the hydrostatic radial bearing so that the spindle can move vertically.

The second feed device consists of the first hydrostatic radial bearing and a hydrostatic axial bearing. The difference between the upper counter pressure and the lower counter pressure of the axial bearings is used so that the spindles are moved precisely.

In the above-mentioned double-head grinding machine according to the present invention, the axial line of the upper spindle and the axial line of the lower spindle are advantageously aligned with each other, and the axial lines of the upper and lower motors for rotating the upper and lower spindles, the first feed device and the second feed device are aligned with the axial lines of the upper and lower spindles.

The structure in which the axial lines of the above six units are aligned with the axial lines of the spindles means a structure in which the axial lines of drive sources are aligned with those of the spindles, instead of the structure in which Motors for rotating the spindles are arranged on the side of the spindles to rotate the spindles with belts. That is, the above-mentioned structure can be implemented with built-in motors. Furthermore, the drive source for generating the force for rotating the first feed device and the linear reciprocating motion conversion mechanism are arranged so as to be aligned with each other. Moreover, the second feed device is structured so that the force for the feeding operation is generated on the same axial line. Thus, the upper and lower spindles, the upper and lower first and second motors, and the first and second feed devices are arranged so as to be aligned with each other. Due to the above-mentioned structure, the overall structure of the grinding machine is structured symmetrically with respect to the axial lines of the spindles. Therefore, very stable mechanical rigidity can be achieved, and extremely precise grinding operation can be carried out.

The nature, utility and principle of the invention will be more clearly understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional view showing a main portion of an embodiment of a twin-head grinding machine according to the present invention;

Fig. 2 is an enlarged sectional view showing a pressure regulator of a grinding wheel feeding unit;

Fig. 3 is a sectional view showing a functional state of the unit shown in Fig. 2;

Fig. 4 is a perspective view showing a main portion of a device for adjusting the horizontal inclination of a lower grinding wheel;

Fig. 5 is an enlarged sectional view showing a pressure regulator of a horizontal tilt adjusting device;

Fig. 6 is a sectional view taken along the line VI-VI shown in Fig. 5;

Fig. 7 is a sectional view showing a functional state of the unit shown in Fig. 6;

Fig. 8 is a diagram showing the function of the pressure regulator of the grinding wheel feed unit;

Fig. 9 is a diagram illustrating a function of feeding a bench for a grinding wheel performed by the pressure regulator;

Fig. 10 is a diagram illustrating a function of a pressure regulator for the lower grinding wheel holder;

Fig. 11 is a diagram showing a function of the pressure regulator for feeding the grinding wheel holder;

Fig. 12 is a front view schematically showing a double-head grinding machine as a second embodiment of the present invention;

Fig. 13 is a side view showing the double head grinding machine;

Fig. 14 is a sectional view showing an upper grinding wheel driving unit of the twin-head grinding machine according to the present invention;

Fig. 15 is a cross-sectional view showing a hydrostatic radial bearing of the upper grinding wheel drive unit;

Fig. 16 is a sectional view showing a lower grinding wheel driving unit;

Fig. 17 is a plan view showing a workpiece support unit; and

Fig. 18 is a sectional view showing a main portion of the workpiece support unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the double-head grinding machine according to the present invention will be described below with reference to the drawings.

A lower spindle head 11 is mounted on a lower frame (not shown) as shown in Fig. 1. A lower spindle 12 is rotatably supported in the central portion of the lower spindle head. A lower grinding wheel 13 is mounted via a grinding wheel holder 14 formed integrally with the upper end portion of the lower spindle 12. A correction motor 15 which is rotated when the grinding wheel is corrected with a dressing operation is mounted on the side surface of the lower spindle head 11. When the correction motor 15 is rotated, the lower grinding wheel 13 is rotated via a pulley 16, a belt 17, a pulley 18 and a lower spindle 12 to carry out the correction of the grinding wheel 13. A lower machining motor 91 which rotates the grinding wheel holder 14 is enclosed in the lower spindle head 11 so that the lower grinding wheel 13 is rotated at high speed when the workpiece is machined.

A workpiece holder 19 is arranged on a lower frame so that the workpiece holder 19 is arranged at a position adjacent to the lower grinding wheel 13. A workpiece holding through hole 20 is formed in the central portion of the workpiece holder 19. A workpiece 21 is inserted into the workpiece holding through hole 20 of the workpiece holder 19 so that a projection formed on the workpiece holder 19 (not shown) and a groove formed on the workpiece 21 are engaged with each other. Thus, the workpiece 21 and the workpiece holder 19 are rotated by a motor (not shown). When a machining operation is carried out, the workpiece 21 is rotated at a low speed. Furthermore, the bottom of the workpiece 21 is attached to the lower grinding wheel 13.

The upper spindle head 22 is mounted on an upper frame (not shown) so that the upper spindle head 22 can be moved vertically so that the upper spindle head 22 is located above the lower spindle head 11. In order to extend the upper spindle 23 in alignment with the lower spindle 12 when the workpiece 21 is machined, the upper spindle 23 is rotatably supported in the central portion of the upper spindle head 22 via pairs of hydrostatic radial bearings 24 and 25 and hydrostatic thrust bearings 26 and 27. An upper grinding wheel 28 is mounted on a grinding wheel holder 29 which is integrally formed with the lower end of the upper spindle 23.

The hydrostatic radial bearings 24 and 25 have supply openings 24a and 25a for supplying oil serving as a pressure fluid to the outer surface of the upper spindle 23. The hydrostatic thrust bearings 26 and 27 have supply openings 26a and 27a for supplying oil to the two opposing drain surfaces of a flange portion 23a of the upper spindle 23.

A grinding wheel correction motor 30 is mounted on the side surface of the upper spindle head 23. When the motor 30 is rotated, the upper grinding wheel 28 is rotated at a low speed via a pulley 31, a belt 32, a pulley 33, and the upper spindle 23.

An upper machining motor 90 is enclosed in the upper spindle head 22 so as to rotate the upper grinding wheel 28 at high speed when the workpiece is machined. A grinding wheel feed motor 34 is mounted on an upper frame (not shown). When the motor 34 is rotated, the upper spindle head 22 is rapidly fed to a position near the workpiece 21 via a ball screw 35 and is then fed to a predetermined machining position at low speed via a guide (not shown).

A hydrostatic pump 36, which is a fluid supply source, is connected to the supply openings 24a and 25a of the hydrostatic radial bearings 24 and 25 and the supply openings 26a of the hydrostatic axial bearings 26 via a supply pipe channel 37 and to the supply opening 27a via a supply pipe channel 39. The fluid under a predetermined pressure is supplied from the hydrostatic pump 36 to the supply openings 24a, 25a, 26a and 27a via the supply pipe channels 37 and 39.

A pressure regulator 38 acting as a pressure regulating device is connected to the feed pipe passage 39 extending from the hydrostatic pump 36 to the feed port 27a of the hydrostatic thrust bearing 27. After the upper spindle head 22 is rapidly advanced to a position near the workpiece 21 by the motor 34 and the ball screw 35, a grinding operation is started so that the upper spindle head 22 is precisely fed. Then, the pressure regulator 38 regulates the pressure of the fluid supplied to the feed port 27a of the hydrostatic thrust bearing 27 from the hydrostatic pump 36. Thus, the upper spindle 23 is further precisely fed so that the upper grinding wheel 28 is moved downward a short distance to the predetermined grinding position.

A fluid inlet port 41 and a fluid outlet port 42 are formed in the outer surface of a housing 40 of the pressure regulator 38, as shown in Fig. 2, spaced apart by a predetermined distance. An adjusting rod 43 is movably inserted into the housing 40. A small diameter portion 43a and a large diameter portion 43b are provided on the outer surface of the adjusting rod 43. When the adjusting rod 43 is moved to the left, the large diameter portion 43b is moved to the left to a region between the fluid inlet port 41 and the fluid outlet port 42, as shown in Fig. 3. Thus, a throttle passage 44 is formed between the fluid inlet port 41, the fluid outlet port 42, and the small diameter portion 43a.

A regulator motor 45 constituting an adjusting member is mounted as an adjusting device on the outer surface of the housing 40. A ball screw 46 is rotatably supported by the outer surface of the housing 40 via a bearing member 47 so as to be connected to a motor shaft of a regulator motor 45 via a coupling 48. A nut 49 is mounted on an outer end of the adjusting rod 43 via a connecting plate 50 and then threadably engaged with the ball screw 46. An encoder 51 is mounted on the regulator motor 45 to detect an amount of movement of the adjusting rod 43 corresponding to the number of revolutions of the regulator motor 45. A cover 52 is mounted on the housing 40 to cover the regulator motor 45, the encoder 51, the ball screw 46 and the nut 49.

When the regulating motor 45 is rotated in a state where the small diameter portion 43a of the adjusting rod 43 is located between the fluid inlet port 41 and the fluid outlet port 42 as shown in Fig. 2, the adjusting rod 43 is moved to the left in Fig. 2 by the ball screw 46 and the nut 49. As a result, the large diameter portion 43b of the adjusting rod 43 is moved to a position between the fluid inlet port 41 and the fluid outlet port 42 as shown in Fig. 3. Thus, the throttle passage 44 is formed between the fluid inlet port 41, the fluid outlet port 42 and the small diameter portion 43a. The length of the throttle passage 44 is changed according to the distance by which the adjusting rod 43 has been moved. Therefore, as shown in Fig. 1, the pressure of the fluid supplied to the supply port 27a of the hydrostatic thrust bearing 27 is lowered in accordance with the length of the throttle passage 44 thus formed. As a result, the bearing balance of the upper spindle 23 in the axial direction, which is produced by the two hydrostatic thrust bearings 26 and 27, is changed so that the upper grinding wheel 28 is precisely fed downward.

A horizontal inclination adjusting unit 53 is arranged, as shown in Figs. 1 and 4-7, so as to correspond to the grinding wheel holder 14 of the lower grinding wheel 13, the horizontal inclination adjusting unit 53 having a plurality of (in this embodiment, for example, eight) pressure regulators 54 formed on the lower spindle head 11 spaced apart from each other by predetermined intervals. The pressure fluid is supplied from the hydraulic pump 36 to the lower surface of the grinding wheel holder 14 of the lower grinding wheel 13 via the supply pipe passage 37, valves 70 and the pressure regulators 54. The pressure of the fluid, i.e., each of the pressure regulators 54, is adjusted so as to adjust the horizontal inclination of the lower grinding wheel 13. The plurality of pressure regulators 54 correspond to the plurality of valves 70.

That is, a fluid inlet port 56 connected to the supply pipe passage 37 extending from the hydraulic pump 36 is formed at one end of a housing 55 of the pressure regulator 54. Further, a fluid outlet port 57 capable of communicating with the bottom of the grinding wheel holder 14 is formed in the outer surface of the housing 55. An adjusting rod 58 is rotatably inserted into the housing 55. A fluid passage 59 capable of communicating with the fluid inlet port 56 is formed in the central portion of the adjusting rod 58. Further, a throttle passage 60 capable of communicating with the fluid passage 59 and the fluid outlet port 57 is formed on the outer surface of the adjusting rod 58. The use of the horizontal inclination adjusting unit 53 is very effective and useful for preventing the workpiece 21, the grinding wheel and the members around them from being heated, since the adjustment of the horizontal inclination of the grinding wheel on the order of micrometers can be carried out with the horizontal inclination adjusting unit 53. It should be noted that this heat generation occurring between the workpiece and the grinding wheel rotated in an inclined state was unavoidable with the prior art, particularly a prior art employing mechanical means (such as a lifting device).

An adjusting motor 61 is attached to one end of the housing 55 via a bracket 62. A motor shaft of the adjusting motor 61 is connected to the adjusting rod 58 via a coupling 63. An encoder 64 is attached to the adjusting motor 61 to detect the amount of rotation of the adjusting rod 58 corresponding to the number of revolutions of the adjusting motor 61.

The adjusting rod 58 is rotated, as shown in Figs. 1, 6 and 7, by the adjusting motor 61 of a pressure regulator 54 which is selected in advance by a control device (not shown). Thus, the length of the throttle passage 60 located between the fluid passage 59 and the fluid outlet port 57 is changed. The pressure of the fluid supplied to the bottom of the grinding wheel holder 14 via the fluid outlet port 57 of the selected pressure regulator 54 is changed, so that the horizontal inclination of the lower grinding wheel 13 is precisely adjusted.

The function of the double head grinding machine with the above structure is described below:

When the double-head grinder is operated to perform the grinding operation, the workpiece 21 is brought to a position where the workpiece 21 is brought into contact with the lower grinding wheel 13 in a state where the workpiece 21 is rotatably held by the workpiece holder 19, as shown in Fig. 1. In the above-mentioned state, the lower grinding wheel 13 is the lower machining motor 91. Further, the upper grinding wheel 28 is rotated by the upper machining motor 90. The upper spindle head 22 is moved downward by the grinding wheel feed motor 34 via the ball screw 35 so that the upper grinding wheel 28 is quickly moved to the position near the workpiece 21. Then, the feed mode is switched to the slow mode for the machining operation so that the upper grinding wheel 28 is fed to the predetermined machining position.

When the feeding operation is carried out by the grinding wheel feeding motor 34 and the ball screw 35, the small diameter portion 43a of the adjusting rod 43 of the pressure regulator 38 is positioned between the fluid inlet port 41 and the fluid outlet port 42. Thus, the throttle passage 44 between the fluid inlet port 41, the fluid outlet port 42 and the small diameter portion 43a is not present. Therefore, oil under a predetermined pressure is supplied from the hydraulic pump 36 to the upper hydrostatic thrust bearing 26 via the supply pipe passage 37. Further, the fluid under the mentioned pressure is supplied to the lower hydrostatic thrust bearing 27 via the supply pipe passage 39 and the pressure regulator 38. Therefore, the upper spindle 23 is rotationally supported by the two hydrostatic thrust bearings 26 and 27 so that the predetermined balance in the axial direction is maintained.

Then, the adjusting rod 43 is moved to the left as shown in Fig. 3 by the regulating motor 45 of the pressure regulator 38. Thus, the large diameter portion 43b is moved so that the throttle passage 44 is formed in the housing 40 at a position between the fluid inlet port 41 and the fluid outlet port 42. The length of the throttle passage 44 is changed according to the amount of movement of the adjusting rod 43.

According to the change in length of the throttle passage 44 of the pressure regulator 38, the pressure of the fluid supplied to the lower hydrostatic thrust bearing 27 is reduced as shown in Fig. 8. Since the pressure of the fluid is reduced as described above, the bearing balance of the upper spindle 23, which is effected by the two hydrostatic thrust bearings 26 and 27, is changed. Thus, the upper grinding wheel 28 is moved precisely in submicron units as shown in Fig. 9. Therefore, the upper grinding wheel 28 is moved exactly to the specified grinding position.

According to the relationship between the length of the throttle passage 44 and the amount of movement of the spindle as shown in Figs. 8 and 9, the length of the throttle passage, i.e., the relationship between the number of rotations of the regulating motor 45 and the amount of movement of the upper spindle, can be determined. Thus, the upper spindle 23 can be precisely adjusted.

An influence of a pressure curve shown in Fig. 8 causes, as shown in Fig. 9, relatively large feed in a region A in the precision feed process. In the region B, relatively small feed can be performed in the precision feed process. Therefore, the region B is used to perform a final stage of feeding the grinding wheel.

The relationship between the length of the throttle passage 60 of the plurality of pressure regulators 54 and the pressure of the fluid at the fluid outlet port 57 of the pressure regulators 54 as shown in Fig. 10 can be determined. According to the determined relationship, the relationship between the length and the amount of downward deviation of the corresponding portion of the grinding wheel holder 14 brought into contact with the pressure regulators 54 as shown in Fig. 11 can be determined.

Thus, the relationship between the length of the throttle passage 60, i.e., the adjustment motor 61, and the amount of downward displacement of the contact portion of the grinding wheel holder 14 can be determined. When a predetermined pressure regulator 54 is selected from the plurality of pressure regulators 54, the precise angle of inclination of the grinding wheel holder 14 and the lower grinding wheel 13 can be adjusted.

The following describes an effect that can be achieved with the above implementation.

The double-head grinding machine according to this embodiment is constructed such that the upper spindle 23 of the upper grinding wheel 28 is rotatably supported by the upper spindle head 22 via the hydrostatic thrust bearings 26 and 27. The pressure regulator 38 serving as a pressure regulating device is provided and regulates the pressure of the fluid to be supplied to the supply port 27a of the supply port 26a and 27a of the hydrostatic thrust bearings 26 and 27.

Since the pressure of the fluid to be supplied to the supply port 27a of the hydrostatic thrust bearing 27 is regulated by the pressure regulator 38, the upper grinding wheel 28 can be accurately fed to the predetermined grinding position. Furthermore, a stable and precise grinding operation can be carried out.

The double-head grinding machine according to the present embodiment is constructed such that the pressure regulator 38 is provided with the regulating motor 45 for changing the throttle passage 44 and the length of the throttle passage 44. When the length of the throttle passage 44 is changed by the rotations of the regulating motor 45, the pressure of the fluid supplied to the supply port 27a of the hydrostatic thrust bearing 27 can be easily adjusted. Thus, the upper grinding wheel 28 can be accurately fed.

The double-head grinding machine according to this embodiment has the horizontal inclination adjusting unit 53 corresponding to the grinding wheel holder 14 of the lower grinding wheel 13. Thus, the pressurized fluid is supplied to the bottom of the grinding wheel holder 14 of the lower grinding wheel 13 via each of the pressure regulators 54 of the horizontal inclination adjusting unit 53. When the pressure of the fluid discharged via the selected pressure regulator 54 is changed, the angle of inclination of the lower grinding wheel 13 can be adjusted. Therefore, the lower grinding wheel 13 can be set substantially parallel to the upper grinding wheel 28, so that the upper and lower grinding wheels 28 and 30 can machine the top and bottom surfaces of the workpiece 21 accurately and in parallel.

The following modification of the embodiment of the present invention will be described.

The above embodiment may be constructed such that the supply pipe passage 37 is connected to the lower hydrostatic thrust bearing 27 to supply the fluid under the predetermined pressure. Furthermore, the pressure regulator 38 may be connected to the upper hydrostatic thrust bearing 26 to regulate the pressure of the fluid to be supplied to the supply port 26a.

A further modification of the above embodiment may be employed in which the pressure regulator 38 is connected to the upper and lower hydrostatic thrust bearings 26 and 27 to individually regulate the pressure of the fluid to be supplied to each of the supply ports 26a and 27a.

A modification of the above embodiment may be used in which the means for regulating the pressure of the fluid to be supplied to the hydrostatic thrust bearings 26 and 27 is a pressure regulator 54 with a rotatable adjusting rod 58 as shown in Figs. 5 and 7, instead of the pressure regulating valve 38 with the displaceable adjusting rod 43 as shown in Figs. 2 and 3.

A modification of the above embodiment may be used in which an operating handle or an operating button is connected to the ball screw 46 instead of the regulating motor 45 of the pressure regulator 38 for the grinding wheel feed unit in order to move the adjusting rod 43 by manually operating the operating handle or the operating button.

The above embodiment may be modified such that an operating handle or an operating button is connected to the adjusting rod 58 instead of the adjusting motor 61 of the pressure regulator 54 of the horizontal inclination adjusting unit 53 in order to close the adjusting rod 58 by manually operating the operating handle or the operating button.

Since one aspect of the present invention has the structure described above, the following effect can be obtained.

The grinding machine according to the present invention makes it possible to feed the grinding wheels precisely to predetermined grinding positions. In this way, a precision grinding process can be carried out.

One aspect of the present invention has the structure in which the length of the throttle passage of the pressure regulating device is changed. Thus, the pressure of the fluid to be supplied to the supply section of the hydrostatic thrust bearing can be easily regulated. As a result, the grinding wheel can be fed or advanced precisely.

A second aspect of the present invention has a basic structure comprising:

a first grinding wheel drive unit standing upright in a vertical direction, the first grinding wheel drive unit including a first spindle that is rotatable and a first housing that rotatably supports the first spindle;

a first grinding wheel held at one end of the first spindle;

a first feed device that moves the first housing in the vertical direction, the first feed device having a mechanism for converting rotational motion into linear motion; and

a first hydrostatic radial bearing movably supporting the first housing.

In addition to this structure, the second version described below optionally has a second feed device with which the grinding wheel can be precisely advanced or fed in order to grind the workpiece more precisely.

Furthermore, in this structure according to the second aspect of the present invention, the axial lines of the first and second feed devices are preferably aligned with each other in order to grind the workpiece more accurately.

It should be noted that the basic idea of the structure described above according to the second aspect of the present invention can be applied to both a single-head grinding machine and a double-head grinding machine.

A second embodiment according to the second aspect of the present invention, which has the structure in which the second feed means is optionally provided for the upper grinding wheel drive unit, will be described below. A frame 101 is formed by fixing a table 103 to the top of a bed 102 as shown in Figs. 12 and 13. An opening portion is formed in the center portion of the upper plates 104 and 105 of the bed 102 and the table 103. The upper plate 105 of the table 103 is supported by a holder 106 consisting of a plurality of walls or posts. Furthermore, the upper plate 104 of the bed 102 and the upper plate 105 of the table 103 are substantially parallel to each other.

A grinding wheel drive unit 107 is provided for the upper plate 105 of the table 103. Furthermore, a lower grinding wheel drive unit 108 is provided for the upper plate 104 of the bed 102. The spindles 109 and 110 arranged in the upper and lower grinding wheel drive units 107 and 108, respectively, are arranged in coaxial alignment with each other. An upper grinding wheel U is mounted on the lower side of an upper grinding wheel holder 111 arranged at the lower end of the upper spindle 109, while a lower grinding wheel L is mounted on the upper side of a lower grinding wheel holder 112 arranged at the upper end of the lower spindle 110. Furthermore, a workpiece support unit 113 is arranged between the upper and lower grinding wheels U and L.

The upper grinding wheel drive unit 107 provided for the table 103 is, as shown in Fig. 14, constructed such that a cylindrical upper housing 115 which can be moved vertically by a first feed device 116 is arranged in a cylindrical upper guide 114 which is fixed to the table 103. The upper spindle 109 which is rotated by a first motor 117 and which can be moved vertically by a second feed device 118 is arranged in the upper housing 115. Furthermore, the upper housing 115 is driven by a first hydrostatic Radial bearing 119 with respect to the upper guide 114, as shown in Fig. 15.

The first motor 117 that rotates the upper spindle 109 is a built-in motor arranged in the upper housing 115. A stator of the first motor 117 is fixed to the inner surface of the upper housing 115, while a rotor thereof is fixed to the outer surface of the upper spindle 109. Since both the upper housing 115 and the upper spindle 109 have a round cross-sectional shape, the axial line of the first motor 117 and that of the upper spindle 109 are aligned with each other.

The first feed device 116 is a mechanism for converting rotations of the motor into a linear reciprocating motion in the vertical direction. A second motor 121 is, as shown in Fig. 14, fixed to an upper cap 120 covering an upper end opening of the upper guide 114, such that the axial line of the motor 121 is aligned with that of the upper spindle 109. A first ball screw 123 is connected to an output shaft 122 of the second motor 121 through a coupling 124. There is also a first nut portion 126 for an upper cover 125 fixed so as to cover the upper opening of the upper housing 115. The first ball screw 123 is threadably engaged with and attached to the first nut portion 126. When the second motor 121 is rotated, the upper housing 115 is moved vertically in the upper guide 114 via the first hydrostatic radial bearings 119a and 119b, the upper housing 115 being supported by the first hydrostatic radial bearings 119a and 119b.

The first hydrostatic radial bearings 119a and 119b are separated from each other in the vertical direction, as shown in Fig. 14.

In a structure in which the upper housing 115 is rotatably supported by the first hydrostatic radial bearings 119a and 119b, it is possible to support the upper housing 115 via a fluid without contact, so that no frictional resistance occurs between the upper housing 115 and the cylindrical upper guide 114. Furthermore, a rigidity of the members supporting the upper spindle 109 can be increased. so that the upper spindle can be fed or advanced precisely in the submicron range.

Furthermore, the upper housing 115, the second motor 121, the first ball screw 123, a coupling 124 and the first nut portion 126 are coaxial with each other, so that the rigidity of the members supporting the upper screw 109 is further increased and the upper screw can be accurately advanced.

The second feed device 118 is constructed, as shown in Fig. 14, such that the second hydrostatic radial bearing 127, which is arranged in the upper housing 115 above and below the first motor 117, rotatably supports the upper spindle 109. Furthermore, a flange 128 is provided on the lower portion of the upper spindle 109 at a position above the upper grinding wheel holder 111. The outer portion of the flange 128 is supported by hydrostatic thrust bearings 129a and 129b, which hold said outer portion from an upper and a lower position in the vertical direction. A fluid pump 130, which is a hydraulic pump that supplies a pressure fluid to the hydrostatic thrust bearings 129a and 129b and the second hydrostatic radial bearing 127, supplies the pressure fluid through the pressure regulators 131a and 131b. When the pressure regulators 131a and 131b have performed adjustment operations, their back pressures change. The pressure difference is used to accurately move the upper spindle 109 in the vertical direction. The second hydrostatic radial bearing 127 and the hydrostatic thrust bearings 129a and 129b are arranged on the outside of the upper spindle 109. Their axes are aligned with the axial line of the upper spindle 109.

Third and fourth motors 132 and 133 are mounted on the table 103 provided with the upper grinding wheel drive unit 107 in such a way that the output shafts of the third and fourth motors 132 and 133 face downward. Furthermore, the third and fourth motors 132 and 133 are arranged on the line of the diameter of the upper guide 114 so as to face each other. The third motor 132 rotates an arm 134 with a dresser D used when dressing the grinding wheel is carried out. The fourth motor 133 rotates an arm 135 with a sensor S which detects abrasion of the grinding wheel.

The lower grinding wheel drive unit 108, as shown in Fig. 16, has a carriage 137 that can slidably move on rails 136 provided for the upper plate 104 of the bed 102. The carriage 137 has a lower guide 138 that extends downward. The lower housing 139 is arranged in the lower guide 138 so that the lower housing 139 can be moved vertically. Furthermore, the lower spindle 110 is rotatably arranged in the lower housing 139. The lower grinding wheel holder 112 is arranged at an upper end that protrudes from the lower housing 139 of the lower spindle 110. Furthermore, the lower grinding wheel L is fixed to the top of the lower grinding wheel holder 112. When the position of the carriage 137 is adjusted, the axial line of the lower spindle 110 is aligned with the axial line of the upper spindle 109, and then a grinding operation is carried out.

The carriage 137 is slidably displaced by a structure formed by engaging a second ball screw 141, which is rotated by a fifth motor 140, which is fixed to the upper plate 104 of the bed 102, with a second nut portion 142 provided for the carriage 137. When the fifth motor 140 is rotated, the carriage 137 is slidably moved along the rails 136. The rails 136 have a guide structure (not shown) such that one of the rails 136 is formed into a V-groove and the other has a flat shape. The carriage 137 is displaced so that it is normally located in the center portion of the bed 102 when the grinding operation is carried out. For example, when dressing is performed on the upper grinding wheel U attached to the upper grinding wheel drive unit 107, the carriage 137 is retracted from the center portion so that the dressing operation can be performed.

The lower housing 139 engages the lower guide 138 so that the lower housing 139 can be moved vertically by means similar to the upper grinding wheel drive unit 107. The lower housing 139 is supported by third hydrostatic radial bearings 143a and 143b with respect to the lower guide 138, as shown in Figs. 15 and 16.

The third hydrostatic radial bearings 143a and 143b are separated from each other in the vertical direction, as shown in Fig. 16.

The lower housing 139 is moved vertically with respect to the lower guide 138 by a first lower feeder 144. Normally, the first lower feeder 144 supports a workpiece W attached to the workpiece support unit 113 at a position where the workpiece must be supported. When the back of the workpiece W is ground, the lower grinding wheel L is moved upward to grind. When dressing is performed, the lower grinding wheel L is moved downward to a position lower than the normal height. The first lower feeder 144 has a short stroke and is constructed so as not to move the lower grinding wheel L vertically during the machining process.

The structure of the first lower feed device 144 is, as shown in Fig. 16, such that a third nut portion 145 is formed to protrude from the outer surface of the lower housing 139. Furthermore, a third ball screw 147 rotated by a sixth motor 146 fixed to the side portion of the lower guide 138 is threadably engaged with the third nut portion 145. When the sixth motor 146 is rotated, the lower housing 139 can be moved vertically.

The structure described above is designed such that the axial line of the first lower feed device 144 is substantially parallel to the lower spindle 110. The structure according to the invention is not limited to this. The structure of the first feed device 116 of the upper grinding wheel drive unit 101 may be designed in the reverse way (not shown) so that the axial line of the first lower feed device 144 coincides with the axial line of the lower spindle 110.

Furthermore, as shown in Fig. 16, a lower second feed device 300 substantially corresponding to that of the upper grinding wheel drive unit 107 is provided. That is, a flange extending radially from the lower spindle 110 is provided on the upper portion of the lower spindle 110 at a position below the upper grinding wheel holder 111. The outer portion of the flange 700 is supported by hydrostatic thrust bearings 300a and 300b which support said outer portion from an upper and a lower position in the vertical direction. A fluid pump 500, which is a hydraulic pump that supplies pressure fluid to the hydrostatic thrust bearing 300a and the second hydrostatic thrust bearing 300b, supplies pressure fluid via the pressure regulators 400a and 400b. When the pressure regulators 400a and 400b have performed adjustment operations, their back pressures are changed. The pressure difference is used to precisely move the lower spindle 110 in the vertical direction. The second hydrostatic thrust bearings 300a and 300b and the hydrostatic radial bearings 600a and 600b are arranged on the outside of the lower spindle 110 to support it. Their axes are aligned with the axial line of the lower spindle 110.

The lower spindle 110, which is engaged with the inner portion of the lower housing 139, is rotated at high speed by the built-in type seventh motor 148 when the grinding operation is carried out. Like the upper grinding wheel drive unit 107, the built-in type seventh motor 148 has a stator fixed to the inner surface of the lower housing 139 and a rotor fixed to the outer surface of the lower spindle 110. Thus, the axial line of the motor 148 is aligned with the axial line of the lower spindle 110, that is, the seventh motor 148 is arranged coaxially with the lower spindle 110.

The workpiece support unit 113 is arranged above the upper plate 104 of the bed 102, and the workpiece support unit 113 is arranged above the lower grinding wheel L installed on the lower spindle 110. The workpiece support unit 113 is configured such that a stationary table 149 is arranged on the upper plate 104 of the bed 102. Furthermore, a horizontal guide 150 is fixed above the stationary table 149 so as to be substantially parallel to the stationary table 149 and at the same time separated from it by a predetermined distance. A slide table 151, which is slidably moved on the top of the horizontal guide 150 in the same direction in which the carriage 137 supporting the lower grinding wheel drive unit 108 is slidably moved, is moved by a fourth ball screw 153 rotated by an eighth motor 152 fixed to the stationary table 149, as shown in Fig. 17. Note that the slide table 151 is formed in a frame shape with a circular opening formed in a rectangular plate.

A plurality of guide rollers 154 each having a V-groove are arranged around the periphery of the circular opening in the slide table 151 at equal intervals in the circumferential direction of the circular opening. The guide rollers 154 rotatably support a rotary frame 155 in a ring shape. A driven gear 156 is formed on the outside of the rotary frame 155 as shown in Fig. 18. A main drive gear 158 provided for a shaft of a ninth motor 157 provided for the slide table 151 is engaged with the driven gear 156 so as to be rotated when the rotations of the ninth motor 157 have started. Furthermore, a support plate 159 is fixed to the bottom of the rotary frame 155 so as to cover the interior of the rotary frame 155. The support plate 159 is formed by a plate having a thickness smaller than that of the workpiece W. The support plate 159 is under tension in the horizontally outward direction so that bending and deformation of the support plate 159 due to the dead mass are prevented. Furthermore, an insertion hole 160 for detachably inserting the workpiece W is formed at the central portion of the support plate 159. An engaging portion 161 in the form of a projection is formed at the inner end of the insert hole 160 for transmitting the rotational force to the workpiece W. Furthermore, the workpiece W has an engaging portion H in the form of a recess called a "notch" which engages with the engaging portion 161. The workpiece W is received in the insertion hole 160 from an upper position so that it is set on the lower grinding wheel L attached to the lower spindle 110. The workpiece W sometimes has a cut portion (not shown) called an alignment flange. In this case too, a means for transmitting the rotational force to the workpiece W is similar to that used when the notch is provided.

Therefore, when the workpiece W is inserted and the ninth motor 157 is rotated, the rotary frame 155 is rotated by the main drive and driven gears 158 and 156, respectively. Thus, the workpiece W inserted into the insertion hole 160 of the support plate 159 provided for the rotary frame 155 is rotated in synchronism with the rotation of the rotary frame 155.

The structure is as described above. The workpiece W is placed on the lower grinding wheel B, and then the second motor 121 is rotated so that the upper housing 115 is moved downward rapidly. When the upper grinding wheel U has approached the top of the workpiece W, the first and seventh motors 117 and 148, which are built-in motors, are rotated to rotate the upper and lower spindles 109 and 110. Thus, the downward movement speed of the upper housing 115 is considerably slowed down, so that a suitable grinding operation is carried out.

With the operation described so far, since the upper housing 115 is rotatably supported by the first hydrostatic radial bearings 119a and 119b when the upper housing 115 is separated from the upper guide 114, it is possible to grind the workpiece accurately in the submicron range.

However, when the workpiece is to be ground more precisely, the rotations of the second motor 121 of the first feed device 116 are stopped. That is, the back pressure acting on the flange 128 of the lower hydrostatic thrust bearing 129a of the hydrostatic radial bearings 129a and 129b is moderately reduced. Thus, the upper grinding wheel U is moved downward in submicron units. Due to the above-mentioned downward movement, very precise finishing is carried out.

The structure of the second lower feeder provided for the lower grinding wheel drive unit 108 is made in a form (not shown) similar to the second upper feeder 118, but the structure is reversed. In this case, the workpiece W is set on the workpiece support unit 113, and then the upper grinding wheel U is moved downward by the first feeder 116 of the upper grinding wheel drive unit 107. Thus, the workpiece W is held between the upper and lower grinding wheels U and B, and then the upper and lower grinding wheels U and L and the workpiece W are rotated. The lower grinding wheel L is slowly moved upward by the first lower feeder 144 so that grinding is carried out accurately. Then, the second lower feeder is operated as required so that the precision grinding operation is carried out. This is how finishing or more precise grinding is carried out to create a specified condition.

When the first and second feed devices 116, 118, 144 are provided for the upper and lower grinding wheel drive units 107 and 108, the two sides of the workpiece W can be simultaneously and accurately finished with the upper and lower second feed devices.

In the above description of the second embodiment according to the present invention, the double-head grinding machine is explained. However, it goes without saying that the embodiment can be applied to a single-head grinding machine.

Since the grinding machine according to the present invention includes a first grinding wheel drive unit standing upright in a vertical direction, the first grinding wheel drive unit including a first spindle that is rotatable and a first housing that rotatably supports the first spindle, a first grinding wheel held at one end of the first spindle, a first feed device that moves the first housing in the vertical direction, the first feed device having a mechanism for converting rotary motion into linear motion, and a first hydrostatic radial bearing that movably supports the first housing, it is possible to increase the rigidity of the grinding machine and to precisely grind the workpiece in the submicron range.

Furthermore, the grinding machine according to the present invention is constructed to switch between the first feed device capable of performing a high-speed feed operation and the second feed device capable of performing a precise feed operation for grinding a workpiece. Since the feed device suitable for the high-speed feed, the feed for pre-processing and the feed for precision finishing can be selected, the workpiece can be ground very precisely in a short processing time.

The grinding machine according to the present invention is constructed so that the axial line of the ball screw of the first feed device is aligned with the axial lines of the upper and lower spindles. Therefore, the grinding wheels can be stably fed.

The grinding machine according to the present invention comprises the second feed device with the hydrostatic thrust bearings supporting the spindles. The back pressure of the hydrostatic thrust bearing is changed so that the spindles are moved vertically. Therefore, the spindles can be moved smoothly and accurately in the vertical direction. Thus, very precise machining can be carried out.

The grinding machine according to the present invention is constructed so that all of the axial lines of the upper and lower spindles, the motors that rotate the upper and lower spindles, and the first and second feed directions are aligned with each other. Therefore, a mechanically and thermally stable structure can be achieved. Furthermore, a required amount of feed can be accurately realized with the first and second feed devices. Thus, a workpiece can be reliably finished to have a required thickness.

Furthermore, with the grinding method according to the present invention, it is possible to precisely grind a workpiece by a small amount by advancing a grinding wheel.

Claims (11)

1. Grinding machine comprising: a first grinding wheel drive unit (107) in a vertical direction, the first grinding wheel drive unit (107) including a first rotatable spindle (109) and a first housing (115) rotatably supporting the first spindle; a first grinding wheel (U) held at one end of the first spindle; a first feed device (116) which moves the first housing in the vertical direction, the first feed device having a mechanism (121-126) for converting rotary motion into linear motion, characterized by: a first hydrostatic radial bearing (119) supporting the first housing movably in the vertical direction. 2. The grinding machine according to claim 1, wherein the first feed device comprises a motor, a ball screw and a nut portion which are connected to each other, and the ball screw is arranged coaxially with the first housing. 3. Grinding machine according to one of claims 1 and 2, wherein the first grinding wheel drive unit comprises: a second hydrostatic radial bearing (127) provided in the first housing for directly and rotatably supporting the first spindle; and a first hydrostatic thrust bearing rotatably supporting the first spindle. 4. Grinding wheel according to claim 3, further comprising: a first auxiliary feed device that moves the first spindle in a vertical direction, the first auxiliary feed device having a first pressure regulating mechanism that can regulate the pressure of a fluid in the first hydrostatic pressure bearing that rotatably supports the first spindle. 5. A grinding machine according to claim 1, wherein the first hydrostatic radial bearing (119) comprises a plurality of hydrostatic radial bearing sections (119a, 119b) separated from each other in the vertical direction. 6. Grinding machine according to claim 1, further comprising: a second grinding wheel drive unit (108) disposed opposite to the first grinding wheel drive unit and standing upright in a vertical direction, the second grinding wheel drive unit (108) including a second rotatable spindle and a second housing (139) rotatably supporting the second spindle; a second grinding wheel (L) held at one end of the second spindle in a state in which the second grinding wheel is held substantially parallel to and opposite to the first grinding wheel; and a second feed device (144) which moves the second housing in the vertical direction, the second feed device having a mechanism (145-147) for converting rotary motion into linear motion; and a third hydrostatic radial bearing (143) movably supporting the second housing. 7. Grinding machine according to claim 6, wherein the second feed device (144) comprises a motor (146), a ball screw (147) and a nut portion (145) which are connected to each other, and the second housing is arranged coaxially to the ball screw. 8. Grinding machine according to one of claims 6 and 7, wherein the second housing comprises: a fourth hydrostatic radial bearing rotatably supporting the second spindle; and a second hydrostatic thrust bearing which rotatably supports the second spindle. 9. The grinding machine according to claim 8, further comprising: a second auxiliary feed device that moves the second spindle in a vertical direction, the second auxiliary feed device having a second pressure regulating mechanism that can regulate the pressure of a fluid in the second hydrostatic pressure bearing that rotatably supports the second spindle. 10. The grinding machine according to claim 6, wherein the third hydrostatic radial bearing (143) comprises a plurality of hydrostatic radial bearing sections (143a, 143b) separated from each other in the vertical direction. 11. A grinding method using a grinding machine according to claim 1, which comprises the steps of: feeding the housing rotatably supporting the first spindle in the vertical direction, the housing being supported by a hydrostatic radial bearing.